Electric match and explosion initiator containing the same



April 17, 1951 s vo 2,549,533

ELECTRIC MATCH AND EXPLOSION INITIATOR CONTAINING THE SAME Filed June 27, 1945 IN VEN TOR.

Patented Apr. 17, 1951 ELECTRIC MATCH AND EXPLOSION INITI- ATOR CONTAINING THE SAME Boyd J. Sevold, Tamaqua, Pa., assignor to Atlas Powder Company, Wilmington, Del., a corporation of Delaware Application June 27,1945, Serial No. 601,823

3 Claims.

matches and to electric explosion initiators containing them. I

An object of the present invention is an im proved electric match which is resistant to static electric discharges.

Another object of the present invention is an improved electric explosion initiator which .is resistantto static electric discharges.

Further objects of the invention will be apparent from the following description:

Electric explosion initiators usually include a shell into which is charged an explosive material, a firing circuit including a bridge wire, and an ignition composition in contact with at least the bridge wire portion of the firing circuit. An electric current passing through the bridge wire. heats the bridge wire to the point where the ignition composition fires and the initiator is exploded.

One type of firing circuit which has found considerable use is the electric match. An electric match customarily includes two elongated terminal sheets separated by insulating material and electrically connected by means of a bridge wire. The terminal sheets form tabs to which leg wires are fastened, and a match head is formed around the bridge wire portion of the match by dipping it in ignition composition.

For some time it has been recognized that electric explosion initiators may prematurely explode if static electric charges'accumulate and pass between the firing circuit and the initiator shell through the ignition composition.

The present invention provides an electric match of improved static resistancewhich may be simply manufactured.

According to the present invention, atleast one of 'the leg wires instead of being merely fastened to a terminal sheet also extends beyond the point of fastening and over the match head. When a match of this form is used in an initiator, the shortest path between firing circuit and shell lies between the extended leg wire and the shell w'all, rather than between a portion of the match covered by ignition composition and the shell wall. Since static electric charges usually jump through the shortest possible path, the ignitioni composition is protected and a high degree of static protection is obtained by use of the pres ent match.

The invention will be particularly described in connection with the drawing in which is shown a specific embodiment of the invention andin which Figures 1, 2, and 3 represent front, side,

[The present invention relates to electric and back views of the match of the present invention, in which Figure 4 is a sectional view of a detonatorassembled with a match of the present invention, and in which Figure 5 is a View of a modified match of the present invention.

Referring to Figures 1, 2, and 3 of the draw- 7 ing, II represents a front terminal sheet in the form of a metal plate; I3 represents an insulating material which is usually a heavy paper, and I5 represents a back terminal sheet which also is a metal plate. Plate I5 is provided with ears I1 and I 9 which are bent around so as to clip plate I I, insulating material I3, and plate I5 together. Insulating material I3 is shaped so as to bend around with ears I! and I9 separating them from plate I l. Between plates II and I5 runs fine bridge wire 2| which is soldered to each of these plates. The plate and bridge wire assembly is then dipped .in an ignition composition cordingto the present invention these leg wires,

instead of terminating at the point of fixation to the terminal plates, extend down and over match head 23.

' A detonator assembled with the match just described is shown in Figure 4. Metal shell 29 contains-in its bottom portion a charge of secondary detonating explosive 3| and a superposed charge of primary detonating explosive 33. Com:- monly used secondary detonating explosives are such material asftetryl and pentaerythritol tetra-- nitrate, and usual'primary detonating explosives are such materials "as nitromannite, lead azide', and diazodinitrophenol. mary or secondar detonating explosives may be used, or the detonator may be of the single charge type. Over primary'detonating explosive 33 is placed metal inner capsule35. This elef ment may be omitted when primary detonating explosives such as diazodinitrophenol are used, but it is preferably employed for materials such as nitromannite which function better with some confinement. The match, which is generally represented by-31 is located inside an insulating tube 39. Insulating tube 39 is usually made of such materials as paper although other insulating materials may -.be employed. Match 31 is Of course, other pri preferably held in insulating tube 39 by means of a plastic material 4|, such as sulphur. Leg wire 25, covered by insulation 43, is fastened to match 31. Leg wire 21 is obscured in Figure 4 by leg wire 25. The leg wire and match assembly is sealed in the detonator by means of two pours of sealing compounds represented by 45 and 41. Asphaltic compositions and sulphur are commonly employed for this purpose. H

To insure maximum protection against static discharges, it is usually preferred. that leg wires Hand 21 extend over match head 23' to a point approximately flush with its lower end. However, it is only essential that they extendsumciently far that the shortest electrical path be--- tween the shell and firing circuit lies to the extended leg wires, rather than to' a portion of the match which is covered with ignition composition. When metal inner capsules are used, care should be taken that the leg wires do not extend so far that they become grounded upon the capsule.

The match of the present invention provides particularly definite advantages for assembly in the initiators for any positioning of the match head toward the shell wall such as would-occur by inaccurate centering results in a similar movement of adischarge pointand, therefore, protection is afforded regardless of the location of the match head in the initiator assembly.

While it is preferred that both leg wires extend over the match head, as is shown in the drawing, the benefits of the invention are substantially obtained if but one leg wire is so constructed.

' In the modification of the invention illustrated in Figure 5, the leg wire extensions are bent so that they are spaced somewhat from the match head. By this means the gap between the firing circuit and. the shell wall is considerably shortened. This modification shown in Figure 5, how'- ever, requires somewhat more care when inserting the match into an initiator shell to avoid contact of the extended leg wires with the shell and consequent undesirable grounding.

In another modification of the invention, the extended ends of the leg wires are broadened as by hammering, or by attaching plate-like mem-- bers so that protection is provided over a large portion of the match head. Usually, however, the simpler form shown-in Figures 1, 2, and 3 will be entirely adequate, and easierto construct and to assemble in an initiator.

Matches of the present inventionmay be used with electric explosion initiators of other varieties than that specifically described and shownin Figure a of the drawing. For example, the matches may be used with detonators having charges and sealing mechanisms of other descriptions. The matches also find application in. other electric explosion initiators suchas metal electric squibs, and in other devices where electric matches are employed as in electric fuse lighters.

It isto be noted that the matches of the present invention, because the sensitive match head is so directly protected, are especially useful in initiators having plastic or other non-conductive shells". In plastic shell initiators, the static electricity tends to discharge between the firing circuit and some conductor lying outside the: shell, rather than betweenthe firing circuit and the shell.

The description in the present specification has centered chiefly around static electric charges be-- cause they are the type of charge from which the principal difiiculties have been experienced. However, it is apparent that the present invention provides protection against discharging electric currents of other sorts.

. The invention has been specifically discussed in connection with the plate type electric match. It is to be clearly understood, however, that it may be employed with any similar type of match as, for example, theioil type, in which the terminal sheets are metal foils pasted onto the opposite sides of a sheet of insulating material.

It is readily seen that the present invention provides'a means for the simple and easy production of electric matches, and of electric explosion initiators containing them, which are resistant to firing by undesired electric discharges.

What is claimed is: v

1. An electric match comprising a pair of terminal sheets separated by insulating material, a

bridge wire co'nne'ctihgsaid sheets, a match head surrounding said bridge wire, and a separate leg wire fastened to each of said terminal sheets, each leg wire extending beyond its point offastening over said match head and to a point ap proximately flush with the end of said match head.

2. An electric explosion initiator containing an explosive charge, an electric match positioned above said explosive charge, said electric match comprising a pair of terminal sheets separated by insulating material, a bridge wire connecting said sheets, a match head surrounding said bridge wire, and a separate leg wire fastened to each of said'sheets, each said leg wire extending beyond its" point of fastening over said match head, and

to a point approximately flush with the end of said match head. a

3. An electric explosion initiator comprising a metal shell containing an explosive charge,- a metal inner capsule over said explosive charge and contacting said metal shell, an electric match position above said explosive charge, said electric match com-prising a pair-of terminal sheets s'ep= arated by insulating material, a bridge wire cone meeting said sheets, and a match head surround ing said bridge wire, and a separate leg wire fas tened to each of said sheets, each said leg wire extending beyond its point of fastening over said match head, and to apoint approximately flush with said match head.

BOYD J. SEVOLD- streamers CITED The following references are of record in the file of this patent: H V

-UNI-TE-D STATES; PATENTS- Great Britain Sept. 1 5, i943 

